Peptidyl-prolyl cis-trans isomerase NIMA-interacting 4 (PIN4) is a peptidyl-prolyl cis/trans isomerase (PPIase) which interacts with NIMA and is vital for cell cycle regulation. PIN4 has 2 different isoforms: PAR14 and PAR17. Furthermore, Pin4 protein binds to double-stranded DNA under physiological salt conditions.